1. Field of the Invention
The subject invention relates to AM receivers having tunable RF circuits.
2. Description of Prior Art
Persons skilled in the art to which the invention described below is related are at least constructively aware of the technology disclosed in U.S. Pat. Nos. 2,791,685, 3,495,195 and 3,571,724.
So far as is considered pertinent, U.S. Pat. No. 2,791,685 discloses a superheterodyne type receiver wherein a motor is used to drive, in the tuning process, capacitors of RF and converter circuits. During tuning of the receiver to a transmitted carrier signal, a generated AGC voltage is combined with a signal related to the derivative of the AGC voltage to provide a control signal. As the receiver is tuned to the frequency of the transmitted carrier signal, the magnitude of the control signal rises rapidly and this change is used to stop the motor, thereby tuning the receiver to the transmitted carrier signal until the motor is restarted.
U.S. Pat. No. 3,495,195 discloses a varactor tuned RF filter circuit controlled by a digital to analog converter which is driven by a binary counter.
U.S. Pat. No. 3,571,724 discloses a signal seeking receiver wherein varactor diodes are used in tuning circuits of the receiver and a generated step voltage is used to tune the receiver through the frequency band to which the receiver is responsive. The stepping action is interrupted by circuitry responsive to receipt of a transmitted signal.